A double attack in Tehran has killed a leading Iranian nuclear scientist and injured a second, according to the authorities.

Men on motorbikes approached the cars of the two men and stuck magnet-bombs on their windscreens, according to one report, though pictures from the scene showed what seemed to be bullet or shrapnel holes in the car of one of the men.

"Majid Shahriyari was martyred and his wife was injured," state radio said. "Fereydoun Abbasi-Davani and his wife were both wounded."

Both men are thought to have been senior figures at the school of nuclear engineering at Shahid Beheshti University in Tehran.

It is not known whether they would have been directly involved in running the programme to enrich uranium which western countries fear is at the heart of Iranian plans to build a nuclear weapon.

However, Mr Shahriyari is said to have been involved in research to analyse neutrons that could contribute to the development of a new generation of nuclear reactors, for peaceful or military purposes. The head of Iran's atomic energy organisation, Ali Akbar Salehi, confirmed he was involved in a "major project".

According to one report, he was on the United Nations list of individuals subject to international sanctions over the nuclear programme.

Dr Abbasi-Davani was said to be a laser expert and to be a specialist in nuclear isotope preparation. He was also said to work with the defence ministry and to have been a member of the elite Revolutionary Guard.

Iran was quick to blame the west and in particular Israel for the attack.

"The enemy took our dearest flower, but must know that this nation, through resistance and all its might, will make efforts to remove problems and achieve its desires," Mr Salehi said, adding that Mr Shahriyari had been his student.

The interior minister, Mostafa Mohammad Najjar, blamed Mossad and the CIA. "The desperate terrorist act against the two academics shows their weakness and inferiority," he said.

In January, another academic involved in nuclear research, Masoud Ali Mohammadi, was killed in a similar motorbike bomb attack. Again on that occasion Iran blamed Israel and the West, though it was also revealed Mr Mohammadi had recently expressed support for the opposition Green Movement in the country.

The highly political links of the latest two targets would on the face of it make such an opposition allegiance seem unlikely. But Meir Javedanfar, an Israeli-Iranian analyst, said even in their case an internal regime assassination could not be ruled out.

He said dissatisfaction with the regime from the country's nuclear scientists was a "major concern" for the leadership.

Mr Salehi threatened retaliation for the killing.

"Don't play with fire," Mr Salehi said. "The patience of the Iranian nation has limits. If it runs out of patience, bad consequences will await enemies."